The present invention relates to a method for controlling a brake system with anti-lock control and/or traction slip control, wherein the wheel rotational behavior is measured and control signals are derived from the measured values by logical combining and by signal processing. The control signals regulate the wheel slip by decreasing, maintaining constant and increasing or re-increasing the braking pressure. A circuit configuration also is provided for implementing this method which generates control signals to switch multiple-way valves inserted into the pressure-fluid conduits of the brake system.
Brake systems with electronic anti-lock control are known. Systems for traction slip control by brake management also are known. The braking pressure in the wheel brakes of the controlled wheels typically is modulated by means of electromagnetically actuatable multiple-way valves which are inserted into the pressure-fluid conduits. The braking pressure is kept constant by closing these valves, braking pressure is decreased by opening a pressure fluid conduit to a pressure supply reservoir, while simultaneously the pressure-fluid inlet conduits are closed. In known so-called plunger-type brake systems, pressure decrease takes place by volume increase of a chamber connected to the wheel brake in which the pressure fluid is contained.
In present systems rapidly acting multiple-way valves with two or three switch positions are used, and the pressure modulation and/or the magnitude and the speed of the desired pressure variation in the wheel brake is achieved by pulsewise actuation of the valves and by variation of the number of pulses or the ratio between pulse duration and pulse pauses.
The measured values and information for braking pressure control and hence slip control are obtained in known systems exclusively with the aid of wheel sensors which generate electric signals indicative of the wheel rotational behavior. By logically combining the signals supplied by the individual wheel sensors, it is possible to determine the vehicle speed, vehicle deceleration and acceleration, etc. However, direct measurement of the braking pressure in the wheel brakes and/or in the braking pressure generator which could supply important information for brake slip control is not provided for reasons of cost. Thus, the control logic responds to the braking pressure and/or the pressure variation attained by actuation of the valves only from the wheel rotational behavior. Relatively long time periods for evaluation of the data, misinterpretations in certain situations and corresponding impairment of the control result from these known techniques.
It is a general object of this invention to improve the control quality without appreciable increase of manufacturing cost. More particularly, information for the control unit relating to the instantaneous braking pressure in the individual wheel brakes which is modulated by valve actuation is obtained without the use of additional sensors.
This object can be achieved in a method of the type referred to, wherein quantities determining the pressure in the wheel brakes are measured and assessed, and from these measured quantities a wheel pressure pattern which, by approximation, represents the pressure variation in the wheel brake is derived and utilized during wheel slip control and/or braking pressure control. A circuit configuration for implementing this method includes circuits, by means of which the quantities determining the pressure in the wheel brakes are measurable and assessable and which form a wheel pressure pattern. These circuits produce a signal which, by approximation, represents the pressure variation in the wheel brakes and which can be included in the signal processing for generating the braking pressure control signals.